1. Field of the Invention
The invention relates to a process for the metered addition of a fluid medium into a material suspension stream of a headbox in which the material suspension stream in the headbox is distributed across the machine width, fed into a plurality of turbulence-producing conduits, and supplied to the headbox nozzle. Furthermore, a total pressure loss xcex94Ptotal is caused in the region of the turbulence-producing conduits, including at least one intake pressure loss xcex94Pintake created at the entrance to the conduits followed by a graduated pressure loss xcex94Pgrad created at a graduated pressure loss area defined by at least one change in cross-section inside the conduits. Furthermore, the metered addition of a fluid medium occurs in the region of the conduits, between the conduit entrance and the conduit exit.
The invention also relates to a headbox for a paper or cardboard machine having at least one material suspension supply running the width of the machine, at least one turbulence producer having a plurality of conduits through which the material suspension flows, a plurality of metered addition points for a fluid medium in the region of at least one of the conduits and an attached headbox nozzle.
2. Discussion of Background Information
DE 35 14 554 A1, describes a conventional headbox design, wherein FIG. 6 shows a headbox having a suspension supply across the width of the machine and a turbulence producer having several conduits through which a material suspension flows. The conduits have a plurality of metered addition points for introducing a fluid medium into one part of the conduits. Moreover, a headbox nozzle is attached in the turbulence producer.
the German patent also discloses a corresponding process for the metered addition of a fluid medium into a material suspension stream of a headbox in which the material suspension stream distributed across the machine width utilizes a plurality of turbulence-producing conduits which are fed by these to the headbox nozzle. In the region of the turbulence-producing conduits, a total pressure loss is produced that arises from at least the intake pressure loss in the conduits and the subsequent graduated pressure losses from cross-sectional change inside the conduits. The metered addition of the fluid medium occurs in a part of the conduits between the conduit entrance and the conduit exit.
In this conventional design, the main pressure loss of the turbulence-producing conduits occurs in the entrance region of the turbulence inserts, i.e., before the metered addition points of the fluid medium. As a result of this arrangement, changes in the flow rate through the conduits during the metered addition affect the basis weight cross profile and fiber orientation cross profile in a negative manner. One attempt to solve this problem is shown in FIG. 6 of the application cited above, in which a fluid is sprayed into the lateral distributor of the headbox near the entrance opening of a turbulence tube, i.e., before the location of the main pressure loss. This design provides for a very small influence of the metered addition on the total flow rate of the turbulence conduits, but it also has the disadvantage that no clear assignment of the added fluid to a certain turbulence conduit is given, with the working width of the metered addition also depending on the amount of the fluid added.
One object of the invention is to disclose a process for the metered addition of a fluid medium into a material suspension stream of a headbox in the region of the turbulence-producing conduits, in which the metered addition of the fluid medium has the least possible influence on the total flow rate of the respective conduit. It is also an object of the invention to disclose a headbox that is appropriate for performing the process according to the invention.
It is recognized that a fundamentally necessary pressure loss occurs in the conventional headbox designs at a turbulence insert having turbulence conduits and/or turbulence tubes chiefly by intake pressure loss at the transition between the lateral distributor of the headbox and the turbulence insert. Because only a low pressure gradient occurs in the part of the turbulence insert that is connected at the outlet side, metered fluid additions in this region have an intense and undesirable effect on the total flow rate of the respective conduit. The solution to this problem is to substantially reduce the intake pressure loss in relation to the pressure loss arising in the further course of the conduit, by an appropriate design of the turbulence conduit in the entrance region. This allows for the possibility of arranging the metered addition in the conduit at the location where the main pressure loss is placed behind the combination point of the added fluid stream with the main suspension stream inside the conduit. The influence, as a result of the amount of fluid in the metered addition which is added to the main stream, has only a very small effect on the total flow rate.
The invention provides for a process for adding a metered addition of a fluid medium into a material suspension stream of a headbox, in which the material suspension stream in the headbox is distributed across the machine width in a plurality of turbulence-producing conduits that supply the material suspension to the headbox nozzle, such that in the region of the turbulence-producing conduits a total pressure loss xcex94Ptotal is caused which arises from at least one intake pressure loss xcex94Pintake at the entrance to the conduits and which provides for a graduated pressure loss xcex94Pgrad by means of at least one cross-section change inside the conduits, in which the metered addition of the fluid medium occurs in the region of at least one of the conduits, between the conduit entrance and the conduit exit. The invention can ideally provide that at least approximately 50% of the total pressure loss xcex94Ptotal is produced downstream of the metered addition of the fluid medium. Preferably, the portion of the pressure loss that occurs downstream of the metered addition of the fluid medium should amount to no more than approximately 75% of the total pressure loss xcex94Ptotal.
One embodiment provides for approximately 50%-60% of the total pressure loss xcex94Ptotal to be produced downstream of the metered addition of the fluid medium.
This design of the headbox allows the metered addition of fluids, e.g., dilution water, into the turbulence insert of a head box wile causing only the most minimal changes in the local total flow rate at the turbulence insert and, it also allows for a clearly defined width of effect of the metered addition, in the range of normal output quantity, which is essentially independent of the amount of the metered fluid.
According to the invention, it is advantageous for the total pressure loss xcex94Ptotal to be in the range of approximately 0.3xc3x97105 Pa to 8xc3x97105 Pa, with a total pressure loss in the range of approximately 4xc3x97105 Pa to 8xc3x97105 Pa being preferred (Pa representing pascal pressure units). This relatively high total pressure loss allows for a further reduction in the influence of the local total volume stream in the case of different metered additions, for example.
It may also be advantageous for the intake pressure loss xcex94Pintake to be kept low by a venturi cross-section design in the conduit since no separation zones to the inflow ensue.
A further possibility for influencing the pressure loss distribution is by using a wave contour located downstream of the metered addition of the fluid medium in the respective conduit in order to produce the pressure loss. By utilizing the plurality of waves in the wave contour, a high pressure loss can be produced in the narrowest space with a desired turbulence structure, i.e., turbulence with short wavelengths.
Another advantageous embodiment of the process provides for the metered addition of the fluid medium in at least one conduit to occur in the direction opposite to the main flow of the material suspension. This allows an optimal mixing of the added fluid with the main stream of the material suspension.
Ideally, the metered addition of the fluid medium takes place in all conduits of the turbulence producer or at least in conduits which are evenly distributed across an entire web width. Such a design makes it possible to adjust the basis weight cross profile and/or the fiber orientation cross profile by metered additions, e.g., of backwater or another fluid whose concentration differs from the material suspension stream that is distributed across the machine width. With respect to the possibilities for influencing the fiber orientation cross profile, the basis weight cross profile, and also the basis weight profile in the z-direction, reference is made to Applications DE 44 22 907 and DE 196 32 673 A1, the full disclosures of which are incorporated by reference herein.
The invention also includes a headbox for a paper or cardboard machine having at least one material suspension supply running the width of the machine, at least one turbulence producer having a plurality of conduits through which suspension flows, a plurality of metered addition points for a fluid medium in the region of at least one of the conduits, and a subsequent headbox nozzle in which at least one of the conduits of the turbulence producer is constructed in such a way that the portion of the flow resistance downstream of the metered addition point amounts to at least approximately 50% of the total resistance of the conduit.
Preferably, the portion of the flow resistance downstream of the metered addition point should amount to no more than approximately 75% of the total resistance of the conduit. Moreover, a division of the resistances before and after the metered addition point is preferred in which approximately 50% to 60% of the total resistance is arranged downstream of the metered addition point.
Another embodiment of the headbox according to the invention provides for at least one conduit with one metered addition point in the entrance region to have a bezel. The bezel has a depth t relative to an entrance surface in the range of approximately 2 mm to 10 mm, preferably in the range of approximately 4 mm to 6 mm, and a bezel angle xcex1 of between approximately 20xc2x0 and 80xc2x0 relative to the entrance surface.
In another embodiment, the conduit with a metered addition point in the entrance region has a contour in the form of a venturi tube. By designing the entrance in this way, the flow into the turbulence conduit occurs in a resistance-free manner, as much as possible, such that the main resistance can be arranged downstream of the metered addition point of the turbulence conduit.
In still another embodiment of the invention the headbox has an exit flow opening of the metered addition point which is arranged in the opposite direction to the main flow of the material suspension in the conduit. As a result an optimal mixing of the added liquid into the material suspension stream is achieved.
It may be ideal for all conduits of the turbulence producer to have a metered addition point or for the metered addition points to be arranged in an evenly distributed manner across the machine width. This results in a particularly simple design for influencing the fiber orientation cross profile and/or the basis weight cross profile as well as the respective profile in the z-direction of the fibrous material layer that has been created.
It should be understood that the features of the invention named above and to be expanded upon below can be used not only in the combinations mentioned, but also in other combinations, or alone, without departing from the scope of the invention.
According to one aspect of the invention, there is provided a process for a metered addition of a fluid medium into a material suspension stream of a headbox which includes feeding the material suspension in a main flow direction through at least one turbulence-producing conduit to a headbox nozzle, such that the at least one turbulence-producing conduit has an entrance, a graduated pressure loss area, and an exit. A total pressure loss xcex94Ptotal is caused in the at least one turbulence-producing conduit such that the total pressure loss xcex94Ptotal includes at least one intake pressure loss xcex94Pintake formed at the entrance and a graduated pressure loss xcex94Pgrad formed at the graduated pressure loss area. A metered addition of a fluid medium is also provided in a region between the entrance and the exit. At least approximately 50% of the total pressure loss xcex94Ptotal may be produced downstream of the metered addition. The metered addition may brake place between the entrance and the graduate pressure loss area. The graduated pressure loss area may be defined by at least one change in cross-section.
The process allows for the total pressure loss xcex94Ptotal produced downstream of the metered addition of a fluid medium to be set so that it does not exceed approximately 75%. The total pressure loss xcex94Ptotal produced downstream of the metered addition of a fluid medium may be in the range of approximately 50% to 60%. The total pressure loss xcex94_total may be any value in a range of approximately 0.3xc3x97105 Pa to 8xc3x97105 Pa, and preferably, in the range of approximately 4xc3x97105 Pa to 8xc3x97105 Pa.
The process may further provide for creating the at least one intake pressure loss xcex94Pintake by a venturi cross-section. Alternatively, it may provide for creating the at least one intake pressure loss xcex94Pintake by a bezel. The bezel may have a depth xcfx84 in a range of approximately 2 mm to 10 mm and an angle xcex1 of between approximately 20xc2x0 and 80xc2x0. Preferably, the bezel has a depth xcfx84 in a range of approximately 4 mm to 6 mm and an angle xcex1 of between approximately 20xc2x0 and 80xc2x0.
The process provides that the graduated pressure loss area include a wave contour for producing the pressure loss downstream of the metered addition. A transition section is located between the metered addition and the wave contour. The transition section includes a diffuser-like conical section. The metered addition is located in a region of greatest narrowing, such that the region of greatest narrowing is located between the entrance and the wave contour. The metered addition may occur in a direction opposite to the main flow of the material suspension.
Moreover, a plurality of turbulence-producing conduits may be used. Additionally, each conduit of the plurality has a metered addition of fluid medium Alternatively, only some conduits of the plurality have a metered addition of fluid medium. The metered addition of a fluid medium is adjusted on, at least one of, a basis weight cross profile and a fiber orientation cross profile of a manufactured web. The metered addition of a fluid may be located between the entrance and a region of greatest narrowing. The region of greatest narrowing is followed by a first diameter section which is larger than the region of greatest narrowing. The first diameter section is followed by a second larger diameter section. A transition section is located between the region of greatest narrowing and the first diameter section.
According to another aspect of the invention, there is provided a headbox for, one of, a paper and cardboard machine which includes at least one material suspension supply running a width of the machine, at least one turbulence producer having at least one conduit through which a material suspension flows, at least one metered addition point located in the conduit for introducing a fluid medium, and a headbox nozzle located downstream from the at least one turbulence producer for delivering the material suspension. A portion of a flow resistance located downstream of the metered addition point is at least approximately 50% of a total flow resistance of the at least one conduit. The flow resistance downstream of the metered addition point may be designed as no greater than approximately 75% of the total resistance of the at least one conduit. Preferably, the flow resistance downstream of the metered addition point is any value in a range of approximately 50% to 60% of the total resistance of the at least one conduit.
The at least one conduit includes an entrance region located before the metered addition point which is defined by a bezel. The bezel has a depth xcfx84 in a range of approximately 2 mm to 10 mm and an angle xcex1 of between approximately 20xc2x0 and 80xc2x0 relative to an entrance surface of the at least one conduit. Preferably, the bezel has a depth xcfx84 in a range of approximately 4 mm to 6 mm and an angle xcex1 of between approximately 20xc2x0 and 80xc2x0 relative to an entrance surface of the at least one conduit. Alternatively, the at least one conduit also includes an entrance region located before the metered addition point which is defined by a venturi tube contour. A transition section is located between the metered addition of a fluid and a wave contour. The transition section has a diffuser-like conical section. The metered addition of a fluid is located in a region of greatest narrowing, such that this region of greatest narrowing is located between the entrance and a wave contour.
The headbox provides that the at least one conduit comprises a wave contour region located downstream of the metered addition point. The at least one metered addition point includes at least one opening for delivering a fluid medium in a direction opposite to the main flow of the material suspension. The at least one turbulence producer also includes a plurality of conduits through which a material suspension flows. Some of the plurality of conduits have metered addition points. Alternatively, all of the plurality of conduits have metered addition points. Additionally, some of the plurality of conduits are arranged in an evenly distributed manner across the machine width.
According to still another aspect of the invention, there is provided a process for a metered addition of a fluid medium into a material suspension stream of a headbox which includes feeding the material suspension in a main flow direction through a plurality of turbulence-producing conduits to a headbox nozzles, such that the plurality of turbulence-producing conduits have an entrance, a graduated pressure loss area, and an exit. A total pressure loss xcex94Ptotal is caused in the plurality of turbulence-producing conduits such that the total pressure loss xcex94Ptotal comprises at least one intake pressure loss xcex94Pintake formed at the entrance and a graduated pressure loss xcex94Pgrad formed at the graduated pressure loss area. A metered addition of a fluid medium is further provided in a region between the entrance and the exit. At least approximately 50% of the total pressure loss xcex94PTotal is produced downstream of this metered addition.
According to another aspect of the invention, there is provided a headbox for, one of, a paper and cardboard machine, which includes at least one material suspension supply running a width of the machine, at least one turbulence producer having a plurality of conduits through which a material suspension flows, each conduit having the following: a narrowed entrance region which creates an initial flow resistance, a region of greatest narrowing which creates an additional flow resistance, and at least one metered addition point for introducing a fluid medium. The metered addition point is located between the narrowed entrance region and the region of greatest narrowing. A headbox nozzle is also located downstream from the at least one turbulence producer for delivering the material suspension. A portion of a flow resistance located downstream of the metered addition point is at least approximately 50% of a total flow resistance of the at least one conduit.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.